1. Field of the Invention
The invention relates to a liquid crystal display device, and especially relates a reflective liquid crystal display device having at least a function of modulating and reflecting the external light in accordance with the image to be displayed so as to make image-displaying.
2. Description of Related Art
There is disclosed a technology to provide a transmissive liquid crystal display device with the so-called black matrix for covering unnecessary display portions other than the pixels in a publication of Japanese Patent Application Laid-Open No. 10548/98 (U.S. Pat. No. 5,956,103) and the like. In the publication, a light-shielding black matrix is provided to cover the unnecessary display portions, including two series of bus-lines (data signal lines and gate lines) disposed orthogonally to each other and a thin film transistor portion, so as to shield the light transmission in the area excluding pixel electrodes to hide the unnecessary display other than display in pixels. Accordingly, those unnecessary display portions have no influence on the image to be displayed. For example, even if the unnecessary portion behaves bad effect e.g. as if it is in a bright state while the image caused by the pixel (electrode) itself is in an extremely dark state (black displaying state), the bright state will not be engaged in display so as to contribute to increase of the contrast ratio.
However, when such a black matrix is disposed on a front side substrate of the concerned display panel, a region of the black matrix is intended to be arranged to be slightly wider so that the black matrix is prevented from going out of the light-shielded area in aligning the front side substrate with the rear side substrate. Therefore, such the region of the black matrix has a shape of overlapping with the border portions of the pixel electrodes in its plan view, which may deteriorate an aperture ratio of the display panel by the overlapping area.
Even in the case where the black matrix is disposed on the rear side substrate of the concerned display panel, the areas of the pixel electrodes are forcedly invaded more or less so as to be light-shielded reliably by the black matrix. Thus, the aperture ratio will be reduced.
Such a black matrix technology may be also applied to a reflective type liquid crystal display device. However, since the reflective type liquid crystal display device basically does not have a backlight system, the function of the black matrix for the reflective type is not so important as in the case of the transmissive type. As far as the reflective liquid crystal display device concerns, it may be more advantageous not to have a penalty of the aperture ratio by a scheme not to have a black matrix that may invade pixel electrodes. This is because the reflective type display device is to display the image by means of reflecting the external light, so the maximized reflection of the light certainly conveying the image is inherently important, and accordingly it is a fundamental mission for the reflective type display device to make effective use of the externally incident light for bright display.
However, in order to provide the better reflective type of liquid crystal display devices, the aforementioned influence of the unnecessary display portions can not be ignored. For the reflective liquid crystal display device, in the unnecessary display portions, particularly the above-mentioned portion of the two series of bus-lines, an electric potential difference caused between the buss-line and the opposing (common) electrode may undesirably drive a liquid crystal portion existing there between. As a result, the contrast ratio may be reduced, for example, the undesirably driven liquid crystal portion may leak the light during the black displaying so that images which should have been darkly displayed are made brightened.